[llvm-bugs] [Bug 24532] New: Wrong mask generated for _mm_blendv_epi8

via llvm-bugs llvm-bugs at lists.llvm.org
Fri Aug 21 07:01:26 PDT 2015


            Bug ID: 24532
           Summary: Wrong mask generated for _mm_blendv_epi8
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: X86
          Assignee: unassignedbugs at nondot.org
          Reporter: aivchenk at gmail.com
                CC: llvm-bugs at lists.llvm.org
    Classification: Unclassified

Created attachment 14754
  --> https://llvm.org/bugs/attachment.cgi?id=14754&action=edit

Following code works with gcc and clang -O0, but fails on clang -O1:
_mm_blendv_epi8 produces wrong result in that case.

>gcc ../blend.cpp -msse4.2 -O2 -o gcc.exe ; ./gcc.exe
finish blend testing
>clang++ ../blend.cpp -msse4.2 -O0; ./a.out
finish blend testing
>clang++ ../blend.cpp -msse4.2 -O1; ./a.out
Aborted (core dumped)

I tested trunk so far only, but I suspect the issue affects 3.6 as well.

The problem is with wrong mask generated for pblendvb:

        movdqa  (%rsi), %xmm1
        movaps  .LCPI0_0(%rip), %xmm0   # xmm0 =
        pblendvb        (%rdx), %xmm1
        movdqa  %xmm1, (%rdi)

While the actual mask for the intrinsic was 0xff00000000000000ff000000ff000000

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